Last Tuesday, Connor Moran, a limit-the-red-meat, increase-the-greens, eat-salad-for-lunch kind of guy, stopped into a Bronx Dunkin’ Donuts for his usual black coffee, no sugar, no cream.

He walked out with a sandwich of egg and bacon between two halves of a glazed doughnut.

Such is the puzzle of the food industry: American consumers, even otherwise healthy ones, keep choosing caloric indulgences rather than healthy foods at fast-food restaurants.

Public health officials have been pushing fast-food restaurants to offer more nutritious foods to help combat excess weight in the United States, where more than one-third of American adults are obese. And restaurants have obliged by adding healthy menu items. But it’s the sugary, fatty items that are flying — or waddling — out the door.

Then there’s the Glazed Donut Breakfast Sandwich from Dunkin’ Donuts that Moran tried. It was rolled out nationally this month after a Massachusetts test that was a “viral hit,” the company’s executive chef told The Boston Globe earlier this month. “Within days of the test, people were sending pictures, tweeting ‘look what I got!’ or ‘this is so wrong!’ and it was just incredible.”

If unhealthy food is wrong, restaurant visitors apparently don’t want to be right.

McDonald’s chief executive officer, Donald Thompson, said recently that although the chain had devoted one-sixth of its advertising time to salads, they make up 2 to 3 percent of sales, and don’t drive growth. Perhaps it would make more sense to give consumers vegetables by stuffing them inside McWraps, Thompson said.

And while restaurants try lower-calorie options — an egg-white sandwich here, a turkey burger there — the unhealthy stuff is “what consumers order — it’s, quite frankly, on them,” said Darren Tristano, executive vice president at Technomic, a food-industry consulting firm.

Gavan J. Fitzsimons, a professor who studies consumer psychology at Duke’s Fuqua School of Business, has researched the disconnect.

In studies, he has presented participants with a range of menu choices — sometimes just unhealthy items, sometimes neutral items (like a fish sandwich) and sometimes healthy choices like salad. It turned out that including a healthy option did change people’s behavior — by making them eat more unhealthily.

“When you put a healthy option up there on an otherwise unhealthy menu, not only do we not pick it, but its presence on the menu leads us to swing over and pick something that’s worse for us than we normally would,” Fitzsimons said.

Why? Fitzsimons called the phenomenon “vicarious goal fulfillment.” By seeing a healthy menu option at a restaurant, “it basically satisfies that goal to be healthy,” he said, and gives consumers leeway to order what they want.

And health-conscious eaters are the most susceptible to picking unhealthy items when the menu also has healthy ones. “It’s often the ones raising their hands, saying they would pick the salad, those are the ones that are the most at risk when they walk in,” he said.

The road to hell may be paved with good intentions, but so, apparently, is the road to high cholesterol.

It’s a conflict the Nobel-winning economist Thomas C. Schelling described in his book “Choice and Consequence”: “People behave sometimes as if they had two selves, one who wants clean lungs and long life and another who adores tobacco, or one who wants a lean body and another who wants dessert,” he wrote. “The two are in continual contest for control.”

Even when consumers are explicitly told the calories a food contains, it doesn’t change their behavior much.

Brian Elbel, an assistant professor of population health and health policy at New York University’s School of Medicine, studied consumer behavior before and after the city required chain restaurants to post calorie counts in 2008.

He found that 54 percent of respondents in New York City said they noticed the calorie labeling. Of those, less than a quarter said they ate fewer calories as a result.

But their behavior did not, in fact, change. When Elbel analyzed consumers’ receipts, he found that there was no difference in calories consumed, whether people said they responded to the calorie counts or not. Consumers may be engaging in what behavioral economists call hyperbolic discounting, he said. “It’s just easier to imagine what this is going to feel like now, and harder to think through what it feels like later,” he said.

When New York City financed another study after the calorie labeling went into effect, overall, the study found no difference in calories consumed before and after the labeling requirement. But there were specific changes.

While just 15 percent of customers said they used the calorie information, those who did ate 106 fewer calories than those who didn’t. Some chains like McDonald’s and KFC saw significant reductions. But at Subway, which nutrition experts say has one of the healthier menus around, and where a higher-than-average percentage of customers said they read calorie information, the number of calories consumed actually increased, from 749 to 882. The researchers hypothesized this was because Subway was promoting $5 footlong subs at the time, and economic incentives trumped healthy intentions.

“What we’re learning from what’s happening in the industry is, consumers don’t see fast food as a place to eat healthy,” said Tristano, the food consultant. “It’s indulgence that’s important.”

Researchers are thinking of new ways to signal nutritional value: how much exercise it would take to burn off a menu item, symbols like traffic lights, or educational campaigns on understanding calories.

But they are not leaving it up to the restaurants.

“They’re not social service agencies — they’re places that are trying to make money by selling food. That’s their business,” said Marion Nestle, a professor of nutrition, food studies and public health at New York University. “Sugar, salt and fat sells.”

As Thompson of McDonald’s put it, “We’re in this time period where people are defining — quote-unquote — healthy and non-healthy, and the question really is, in the restaurant business, what does the customer want?” he said.

For Hannah Terry-Whyte, an Australian food blogger visiting the United States last week, it wasn’t so much the indulgence she was after as the cultural experience when she ordered the doughnut breakfast sandwich.

“As an Australian, that, to me, is such the epitome of crazy American food behavior that I kind of had to try it,” she said.

Still, even she wasn’t immune to its meat-and-sugar seductiveness. Asked if she would try it again, she said, “You know what? Maybe. Yeah. Probably.”